Fuel systems of motor vehicles, particularly passenger cars and light trucks, utilize a fuel fill pipe which provides a conduit to channel fuel from an exteriorly accessible, selectively closable opening to the fuel tank during a refueling event. The fuel systems of motor vehicles powered with high concentrations of alcohol blended fuels (i.e., greater than twenty percent alcohol blended with gasoline) typically incorporate a flame arrester in the fuel fill pipe disposed up stream of the fuel tank. The flame arrester prevents an ignited mixture of flammable vapors originating at the fuel fill pipe inlet from reaching the fuel tank during refueling. Combustible vapors in alcohol blended fuels can occur at much higher temperatures than would occur for gasoline fuels which contain low concentrations of alcohol, thereby driving the rationale for inclusion of a flame arrester in the fuel system. Flame arresters are used with flex fuel vehicles and other motor vehicles where combustible mixtures of fuel and air can exist in the vehicle fuel system at higher ambient temperatures than regular unblended gasoline. The flame arrester used in the prior art has certain drawbacks, including its being an added piece within the fuel fill pipe, causing flow restriction to the fill pipe, and affecting fuel filling quality. An example of an advanced flame arrester is described in U.S. Patent Application Publication 2008/0271814-A1, published on Nov. 6, 2008.
Motor vehicles equipped with onboard refueling vapor recovery systems utilize a normally biased closed inlet check valve assembly for the fuel system which provides sealing of the fuel chamber of the fuel tank from the fuel fill pipe in reverse of the fill flow direction, wherein the inlet check valve assembly has a valve member that is movable between a fully closed state and a fully open state, the valve member being biased to the normally closed state by light spring force, but, when acted upon by flow of fuel, moves toward the fully open state against the spring biasing.
Referring now to FIGS. 1 through 3, FIG. 1 shows a prior art fuel system 10, applicable by way of example to a flex fuel motor vehicle, incorporating a conventional inlet check valve assembly 12 which may be of a “flapper” type valve member as show by way of example at FIG. 2, or may be of a “shuttle body” type valve member, as shown by way of example at FIG. 3. The inlet check valve assembly 12 is generally disposed at the interface of the fuel fill pipe 14 and the fuel tank 16. The fuel fill pipe 14 provides a conduit to channel fuel 18 being dispensed by a fuel pump nozzle 20 via an exteriorly accessible, selectively closable opening 22 thereof to the fuel chamber 16′ of the fuel tank 16 during a refueling episode. A conventional flame arrester 24 is disposed in the fuel fill pipe 14 between the opening 22 and the inlet check valve assembly 12.
A conventional flapper type valve member inlet check valve assembly 12′ in the fully open state is shown at FIG. 2. The valve member is a flapper (also referred to as a valve door) 26 which carries a seal 26′. The flapper 26 rotates (or pivots) on a spring biased pivot 28 connected with a valve tube 32 relative to the throat in response to flow of fuel 18 and biasing by a spring 30. The valve tube 32 is connected to a throat 36 terminating at a throat mouth 38 which is sealed closed by the seal 26′ when the flapper 26 is at a closed state in response to biasing by the spring 30. When fuel 18 is introduced into the fuel fill pipe (see FIG. 1), pressure exerted on the flapper 26 by the fuel flow overcomes the spring biasing and the flapper assumes the fully open state, as shown. A shroud 34, shown in phantom, may be disposed concentrically in relation to the valve tube at the fuel tank side of the inlet check valve assembly 12′.
A conventional shuttle type valve member inlet check valve 12″ in the fully open state is shown at FIG. 3. The valve member is a shuttle body (also referred to as a valve plunger) 40 which carries a seal 40′. A valve tube 42 has a plurality of fuel dispensing apertures 44 and receives a guide bar 46 of the shuttle body 40 at a partly closed distal end 48. The valve tube 42 is connected to a throat 50 terminating at a throat mouth 52. The shuttle body 40 axially moves (slides) in the valve tube 42 relative to the throat in response to flow of fuel 18 and biasing by a spring 54. The throat mouth 52 is sealed closed by the seal 40′ when the shuttle body 40 is at a closed state in response to biasing by the spring 54. When fuel 18 is introduced into the fuel fill pipe (see FIG. 1), pressure exerted by the fuel flow on the shuttle body 40 overcomes the spring biasing and the shuttle body assumes the fully open state, as shown. A shroud 56, shown in phantom, may be disposed concentrically in relation to the valve tube at the fuel tank side of the inlet check valve assembly 12″.
It is a well known principal of chemistry that a complete combustion reaction with no excess requires a particular ratio of fuel to oxidant defined by the reactants, known as the stoichiometry of the reaction. Accordingly, the combustibility of a fuel and air mixture depends upon the ratio of fuel to air. In an environment in which the ratio is becoming progressively richer, that is, proportionally higher in fuel and lower in air, eventually a point is reached whereat the mixture will no longer support combustion.
The science behind arresting (or quenching) a flame depends upon the ability to remove a flame's heat by providing small passages (with length as a secondary factor) for the flame front to pass therethrough. For fuel and air mixtures, the minimum flame propagation distance between two surfaces in which a flame can still propagate therebetween is a function of both the chemical being combusted (the fuel) and its concentration with respect to air (more precisely, the oxygen in the air). When the distance between the surfaces is reduced below that minimum flame propagation distance, then the flame will be quenched and combustion cannot proceed past that point, even if the fuel to air ratio supports combustion.
Normally, the minimum flame propagation distance is somewhat on the rich side of stoichiometry of the mixture and may be, for example, on the order of about 0.06 to about 0.1 inch. However, for relatively hotter gases, higher pressure gases, and less conductive gases, a smaller minimum flame propagation distance may be required for flame arresting. Geometry also plays an important role. For example, two needle-like point shaped surfaces have a much smaller minimum flame propagation distance than, by way of comparison, the walls of a slit or a tube which flame arrest at the greatest separation therebetween. The range of minimum flame propagation distance for arresting a flame applicable to combustible mixtures of gasoline and air in the atmosphere is from about 0.07 to more than about 0.14 inches. In actual practice of motor vehicle fuels, the fuel and air mixture will be a combination of primarily butane and pentane isomers with some hexane and very small amounts of heavier hydrocarbons, all of which have minimum flame propagation distances for combustible mixtures of fuel and air, generally greater than about 0.1 inch.
In that the fuel to air mixture in a motor vehicle fill pipe will be a quite rich fuel to air ratio (high in fuel and fuel vapor and low in air), the minimum flame propagation distance of this fuel and air mixture in the fuel fill pipe will be accordingly increased over a stoichiometric ratio of fuel to air. However, to protect against untoward flame incidents in extreme cold and with oxygenated fuels, flame arresters utilize the smallest determined minimum flame propagation distance as being applicable.
For further information on flame arresting (or quenching), see NACA report 1300 of 1959, “Basic Considerations in the Combustion of Hydrocarbon Fuels with Air” is the 1959 classic by Barnett and Hibbard, (note of interest: the National Advisory Committee for Aeronautics (NACA) was predecessor to the present National Aeronautics and Space Administration (NASA)).
In view of the foregoing, it would be very beneficial if somehow a separate piece flame arrester as it is known in the prior art could be eliminated, and yet flame arresting/quenching still be provided by the fuel system.